Optical discs are currently used in a variety of ways, including digitally storing computer data, musical compilations or software within the disc. The information stored within the disc is protected by at least one layer of material in such a way that the information may still be read by a laser. Specifically, hundreds of millions of pits are molded into one side of a transparent plastic disc. The pits are arranged so that music or other information is digitally stored in the pits in a helical or spiral pattern, similar to the grooves on a vinyl record. A thin reflective coating or layer is applied to the back of the pits. A protective plastic layer is applied over the reflective layer to protect the coating and the pits. Then a label is applied to the protective layer.
The information stored in these optical discs is read by using one or three laser beams that enter the disc through the transparent plastic (i.e., the "play side" or "read side"). The laser is then reflected back from the reflective layer and passes back through the transparent plastic layer or play side of the disc. When three lasers are used, one reflected laser beam contains the digital information from the pits and is then processed through a device such as a computer, a stereo or a game console. The other two reflected laser beams are used to focus the laser and keep it "on track" as it reads the spinning disc. When only one laser beam is used, the laser reads the data, focuses the laser and keeps the laser on track. In the case of a compact disc, the first track, called the "lead-in" track is a band of data that contains the table of contents for the whole disc. The information in the lead-in track is used by the disc player to quickly locate selected individual songs or other data tracks. Thus, if a person were to select track six on a compact disc, the laser would find the location of track six from the lead in track and then move to that particular location on the disc.
When the play side of the transparent layer is scratched or dirtied, the laser beams may scatter or deviate from their correct optical path as they enter or exit the transparent layer. Such scattering can preclude the proper reading of the data layer. In the case of a compact optical disc, if the tracking beams are scattered, the disc player's closed-loop feedback system might be induced to "thinking" it is off track. It will then try to adjust by jumping either forward or backward. If the player jumps forward, it will "skip" a portion of the music. If the player jumps backward, it will attempt to play until the laser reencounters the scratch and skips backward again. In this way, a portion of data can be repeated indefinitely, causing an obnoxious electronic sound with some players and silence with others. If a scratch limits the readability of the lead-in track, none of the tracks will play because the player would not know where the individual tracks were located.
If only the free surface on the read side of the transparent plastic layer is scratched, the data itself is not harmed. Only the ability to read this data is hindered. Because some disc reading devices allow for the disc to be read even if the transparent layer has certain types of scratches, scratches in optical discs do not necessarily have to be removed completely for a flawless playback. In particular, the size and orientation of the scratch damage to the disc may influence the effect it has on the readability of the disc. For instance, a disc reading device will have a better chance at reading a disc with a radial scratch than a circumferential scratch. A radial scratch would generally be better because the lasers read the information stored in the data layer of the disc in a helical or spiral pattern. Problems thus often can be eliminated by merely smoothing the edges of the scratches and/or reducing their width and depth.
Repairing optical discs requires a level of control that cannot be consistently achieved by hand. Polishing too aggressively can damage discs. Polishing too delicately leaves them unrepaired. Sandpaper kits are often too aggressive and can make a disc unplayable if too much pressure is applied. Polishing solutions are at the other extreme. They use such fine abrasives to avoid burning that they have difficulty repairing even moderate scratches--no matter how much pressure is applied.
The laser disc buffing apparatus disclosed in U.S. Pat. No. 5,423,103 uses a polishing technique to remove light and medium scratches and smooth and diminish more severe scratches. The apparatus was designed to repair play side damage using a radial polishing motion that is much more tolerated by optical disc players. It achieves this radial polishing motion by using a disc-polishing wheel in an orientation that is substantially perpendicular to the disc. It can be a hand-held, manually operated mechanical device or it can be electrically powered.
Preferably, a buffing apparatus would polish with consistent pressure across the entire optical disc radius. This control allows the laser disc buffing apparatus to apply the highest pressure short of burning, resulting in the maximum effectiveness that can be achieved without damage to the optical disc.
It is generally known that when a loop or hoop with thin walls is in the vertical plane and pushed down on a solid, horizontal surface, it exerts a bi-modal force profile on that surface, with less force exerted directly below the center of the hoop and more force exerted on either side of the center point in the plane of the hoop. Also, it is generally known that when a solid disc in the vertical plane is pushed down on a solid, horizontal surface, it exerts a force on the surface that is a maximum directly below the center of the disc and rolls off on either side of the center in the plane of the disc.
In order to eliminate dust and contaminants from a disc surface, it has been known to use materials such as chamois, mohair, felt or cotton to wipe the surface.
It has further been known to fill the scratches by spreading a waxy or other filter material on the disc, then wiping away the excess to repair a damaged disc surface. It has also been known to use a felt cloth in conjunction with an abrasive solution to buff away scratches on an optical disc.